Thermosensitive photothermal agents (AuNRs@pNIPAAm) for accurate temperature control were prepared by covalent binding pNIPAAm to gold nanorods. Stretched pNIPAAm collapses when temperature increases around low critical solution temperature, inducing a redshift of LSPR wavelength. To obtain a high-throughput LSPR scattering spectral mapping of AuNRs@pNIPAAm particles, we demonstrate a spatiotemporal resolution plasmonic spectroscopy (SRPS) which provides the LSPR wavelength of multiple AuNRs@ pNIPAAm particles simultaneously at millisecond level (limited by camera frame rate).
SRPS is performed on a home-made two-channel highly inclined and laminated optical (HILO) sheet dark-field microscope. Nanoparticles with LSPR wavelength of ~750 nm are incubated with cells. Two continuous lasers (with wavelength of 730 and 785 nm, avoid the broadband scattering background from biological environment) are combined and modulated in order to generate a pulse beam. This beam is then directed onto the cover-slide with an appropriate incident angle to generate a HILO sheet, which is suitable for high spatial resolution imaging of nanoparticles inside cell samples. Another 808 nm laser is focused on the sample to heat nanoparticles.
Scattering light of nanoparticles is collected by the same objective, which is recorded by a CMOS camera. CMOS camera and the pulse laser are synchronized in order to capture the dark-field images from two wavelength lasers periodically, which generates a two-channel image sequence. With this configuration, we measure the scattering intensity of nanoparticles illuminated by two lasers simultaneously, which can be further converted to LSPR wavelength image.